Electrostatic chuck assembly

ABSTRACT

An electrostatic support system for retaining a wafer. The support system generally includes a support body having a support surface for retaining said wafer, a voltage source coupled to the support body for electrostatically coupling the wafer to the support surface, and a cooling system for cooling the wafer. A plurality of arm members extend from the support body to a carriage assembly for releasably mounting the support body to the processing chamber with the support body and the arm members separated from the chamber floor. This invention also includes the method of supporting a wafer in a processing chamber which includes the steps of positioning the wafer on a wafer supporting surface, applying a voltage to an electrode assembly to electrostatically attract the wafer to the support surface and, after processing the wafer, substantially grounding the electrode assembly to sufficiently deactivate the electrostatic charge for release of the wafer from the support surface.

This is a continuation of application Ser. No. 08/500,480 filed Jul. 10,1995, now U.S. Pat. No. 5,708,556.

BRIEF DESCRIPTION OF THE INVENTION

This invention relates in general to a method to hold down a conductivemember onto a support surface without contacting the front or sidesurfaces of the conductive member, more particularly, to anelectrostatic clamp for supporting a semiconductor wafer duringprocessing.

BACKGROUND OF THE INVENTION

Various support systems have been employed to support a semiconductorwafer during chemical vapor deposition, sputtering, etching, and otherprocesses. The support systems are often cooled in an attempt tomaintain a substantially constant wafer temperature. Retaining the waferat a constant temperature during processing is important for controllingthe chemical process, obtaining process uniformity, and preventingdamage to the integrated circuitry already formed on the wafer. Thewafer is generally secured to the support to retain the wafer inposition during processing and to improve heat transfer between thewafer and the support surface.

One type of support system employs a perimeter clamping ring whichextends across the peripheral edge of the wafer to retain the wafer inplace. The portion of the wafer beneath the ring is clamped tightlyagainst the support surface. The clamping ring limits the total areaavailable for circuit formation since the peripheral edge of the waferis covered by the ring. The first side contact may introduce impuritiesto the wafewr. Another type of support system electrostatically clampsthe wafer to the support surface. This is accomplished by applying avoltage to the support and inducing an image charge on the wafer. Thedifferent potentials attract the wafer to the support surface, tightlyclamping the entire wafer to the support. The entire surface area of thewafer now becomes available for the formation of integrated circuits. Inaddition, there is no surface contamination.

Electrostatic support systems are typically supported on the bottom ofthe processing chamber. As a result, the system pump must be positionedat another location, for example to the side of the chamber. Thisconfiguration reduces uniformity of the flow of process gases throughoutthe chamber and increases the footprint of the overall system. Removingthe wafer support system from the bottom of the chamber would allow thepump to be axially aligned with the wafer, improving uniformity andreducing the footprint of the processing system.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of this invention to provide an electrostaticsupport assembly for supporting a wafer during processing.

It is a further object of this invention to provide an electrostaticsupport system for supporting a wafer during processing at low pressureswhich provides for the uniform flow of process gases around the wafer.

It is another object of the invention to provide an electrostaticsupport assembly with a cooling system for efficiently maintaining aconstant and uniform wafer temperature during processing.

It is yet another object of the invention to provide an electrostaticsupport assembly in which the wafer may be rapidly and efficientlyremoved from the support assembly.

A more general object of the invention is to provide an electrostaticsupport system which securely retains the wafer during processing whileminimizing the risk of damage to the components on the exposed surfaceof the wafer from excessive heat, transient currents, and prematureseparation of the wafer from the support.

Another general object of the present invention is to provide anelectrostatic support system which allows the entire surface of thewafer to be uniformly exposed to the process gases and which may beefficiently manufactured and operated.

In summary, this invention provides an electrostatic support assemblywhich is particularly suitable for retaining a wafer during processing.The support assembly generally includes a support body having a supportsurface for retaining the wafer, a voltage source coupled to the supportbody for electrostatically coupling the wafer to the support surface,and a cooling system for cooling the wafer. The cooling system includesa plurality of gas distribution grooves formed in the support surfacewhich facilitate the rapid distribution of a gaseous substance betweenthe wafer and the support surface. The cooling system includes arestriction mechanism in the conduit between the gas source and the gasdistribution grooves to prevent catastrophic separation of the waferfrom the support surface in the event a portion of the wafer becomesseparated from the support surface. A plurality of arm members extendingfrom the support body are mountable to the processing chamber with thesupport body and the arm members separated from the chamber bottom.

This invention also includes the method of supporting a wafer in aprocessing chamber which includes the steps of positioning the wafer ona wafer supporting surface of a support body having at least oneelectrode, applying a voltage to the electrode to induce theelectrostatically attractive forces that hold the wafer to the supportsurface and, after processing the wafer, substantially grounding theelectrode to sufficiently deactivate the electrostatic charge forrelease of the wafer from the support surface. In a preferred form ofthe invention, the support body includes two electrodes and the voltageapplying step includes applying a positive voltage to one of theelectrodes and a negative voltage to the other electrode. After thewafer is removed from the chamber, the polarity of the electrodes isreversed for the next wafer. In an embodiment of the invention employedin plasma-enhanced processes, the method also includes the step ofapplying an RF bias to the electrode or combination of electrodes.

Additional objects and features of the invention will be more readilyapparent from the following detailed description and appended claimswhen taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an electrostatic support systemconstructed in accordance with the invention, shown installed in aprocessing chamber.

FIG. 1A is an enlarged, partially broken away view of a reactorincorporating the electrostatic support system of FIG. 1.

FIG. 2 is a top view, partially broken away, of the electrostaticsupport system of FIG. 1, shown supporting a wafer.

FIG. 2A is a top view of another electrostatic support system.

FIG. 3 is a top view of the support surface of the electrostatic supportsystem of FIG. 1.

FIG. 4 is a cross-sectional view taken substantially along line 4--4 inFIG. 3, shown with the lifting pins in an extended position supporting awafer.

FIG. 5 is a bottom plan view of the base of the electrode assembly.

FIG. 6 is an enlarged schematic cross-sectional view, partially brokenaway, of the electrode assembly and DC and RF voltage supplies of theinvention.

FIG. 7 is an enlarged cross-sectional view, partially broken away, ofthe ion focus ring and guard ring of the support body 12.

FIG. 8 is an enlarged cross-sectional view, partially broken away, ofthe lifting mechanism, shown with the lifting pins in the retractedposition and a wafer positioned on the support surface.

FIG. 9 is cross-sectional view taken substantially along line 9--9 inFIG. 4.

FIG. 10 is a cross-sectional view taken substantially along line 10--10in FIG. 8.

FIG. 11 is a cross-sectional view taken substantially along line 11--11of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made in detail to the preferred embodiment of theinvention, which is illustrated in the accompanying figures. Turning nowto the drawings, wherein like components are designated by likereference numerals throughout the various figures, attention is directedto FIGS. 1-2.

FIGS. 1 and 2 generally show an electrostatic support system or chuckassembly which is particularly suitable for retaining a wafer 6 in aprocessing chamber 8 during plasma-enhanced chemical vapor deposition,although the support system 10 may also be used with other types ofprocessing including, but not limited to, chemical vapor deposition,sputtering, etching and the like. The support system 10 is particularlysuitable for use with a high density, plasma enhanced chemical vapordeposition system of the type shown for example in FIG. 1A and disclosedin the co-pending application Ser. No. 08/500,493, incorporated hereinby reference. The support system 10 includes a support body 12 with asupport surface 14 for retaining a wafer and arm members 16 extendingoutwardly from the support body 12 for mounting the body to the chamber.In the present embodiment, arm members 16 are mounted to a carriageassembly 17, which is in turn releasably secured to the chamber 8. InFIG. 1A, the processing chamber 8 is positioned below a plasma assembly9 and includes a gas injection manifold 11 mounted to the chamber 8 forinjecting gaseous substances into the processing chamber. Below thechamber 8 is a vacuum pump 13 coupled to the chamber 8 by a port 15which defines the bottom of the processing chamber. The support system10 is suspended above the bottom of the process chamber, allowing thepump 13 to be substantially axially aligned with the process chamber.During operation, the entire wafer 6 is securely clamped to the supportsurface 14 by an electrostatic force. The uniform contact provided bythe electrostatic clamping controls the heat transfer between the wafer6 and the support surface 14 so that the entire wafer may be retained atthe desired temperature throughout the processing. Maintaining the waferat a uniform temperature is required for achieving the desired filmproperties for material deposition or uniform etch rates for removal ofmaterial.

Support body 12 includes an electrode assembly 20, shown particularly inFIGS. 4-7, which generally defines the support surface. The electrodeassembly 20 is mounted to support base 18 having a removable cover 19 toprovide access to the interior of support body 12 for maintenance andrepair. Suitable seal members are provided at each junction.

The electrode assembly 20 includes an inner electrode 22, an annularouter electrode 24 and an annular guard ring 26 mounted to a base 28which is electrically isolated from the electrodes, but not from theguard ring. The inner electrode 22, outer electrode 24 and guard ring 26are coated with a dielectric material, electrically isolating theelectrodes 22 and 24 from each other as well as the processing chamber.The peripheral edges of the electrodes 22 and 24 and guard ring 26 arepreferably curved so that the dielectric coating may be uniformlyapplied, providing protection against arcing. In the present embodiment,the base 28 is formed of aluminum and coated with a high qualitydielectric coating such as aluminum oxide. However, it will beunderstood that other means may be used for electrically isolating base28 from the electrodes and the guard ring. A fluid channel 30 extendsthrough the base and is enclosed by a cover plate 32 mounted to the base28. As is shown particularly in FIG. 5, the channel 30 snakes across asubstantial portion of the base 28 to provide uniform cooling and toavoid other components of the support body 12. The inlet 31 and outlet33 of the channel are coupled via conduits 35 (FIG. 2) to a fluid source36 for the circulation of a cooling fluid such as water or anothersuitable liquid through the channel. A gasket 34 is compressed betweenthe base 28 and cover plate 32 to form a seal between the base and thecover plate and prevent leakage of the cooling fluid from the base 28.

The channel 30 provides a passageway through the base 28 for a coolingfluid such as water or another liquid through the base 28 forefficiently removing heat from the electrode assembly 20. The electrodeassembly 20 of this invention is of particular advantage in that theelectrodes 22 and 24 and guard ring 26 are electrically isolated fromthe grounding effects of the cooling fluid. Transporting the coolingfluid through the base 28 is preferred as heat may be rapidly removed,eliminating temperature gradients and preserving the planarity ofsupport surface 14. However, in other modifications of the invention theelectrode cooling system may be separate from the base 28 and electrodes22 and 24. Furthermore, it can be used as a means to set the desiredtemperature of the assembly at a process defined temperature.

Electrode system 20 is used to electrostatically attract the wafer 6 tothe support surface 14. As is shown particularly in FIG. 6, theelectrode system 20 includes a first electrical connector 40 couplingthe inner electrode 22 to a voltage source 42 through an RC filter 43and a second electrical connector 44 coupling the outer electrode 24 tothe voltage source 42 through an RC filter 45. The voltage source 42applies a DC bias, with the polarity of the outer electrode 24 beingopposite that of the inner electrode 22. The applied DC potentials onthe electrodes 22 and 24 generate image charges on the back surface ofthe wafer and electrostatically attract the wafer to the support surface14, securely clamping the wafer to the support surface. The polarity ofthe electrodes is reversed by activating gang switch 46 each time awafer is removed from support surface 14 to minimize any residualcharges or polarization in the dielectric coating which may interferewith the release of the wafer from the support surface.

The surface area of the inner and outer electrodes 22 and 24 issubstantially equal, providing a uniform bipolar charge across thesupport system 10. When the support system 10 is used in plasma enhancedsystems, the electrodes 22 and 24 are electrically floating with respectto the plasma to prevent leakage of current to the plasma. Electrodes 22and 24 are preferably referenced by center tapping the electrodes to theguard ring 26, which substantially centers the DC potential around thepotential induced in the wafer by the plasma. As a result, a constantpotential is distributed across the support surface to maintain uniformclamping. In the present embodiment, where the support system 10 is usedin plasma-enhanced processing systems, the wafer has a potential ofabout -300V, for a typical RF bias of 2000 watts. Centertapping theelectrodes 22 and 24 to the guard ring 26 causes one electrode to havepotential of +100V and the other electrode a potential of -700V whencoupled to an 800V voltage source. If the electrodes were centertappedto ground, the potential of the electrodes would be non-uniform withrespect to the biased wafer. If the voltage source has a sufficientlyhigh impedance so that the power supply is fully floating from ground,center tapping the voltage source to the guard ring 26 will beunnecessary because the electrodes 22 and 24 will "self center" aroundthe bias induced in the wafer, accommodating the desired uniformclamping.

The electrodes 22 and 24 preferably have substantially smooth, planarupper surfaces for improved temperature uniformity across the wafer tomaintain the planarity of support surface 14. The increased stabilityprovided by the planarity of the electrode surfaces is particularlyimportant during high-density plasma enhanced processes where the filmdeposition is occurring at the high thermal loads of the wafer wherethermal non-uniformities can cause stress in the wafer leading to waferbreakage. By preventing possible damage to the wafer, the electrodeassembly substantially improves the efficiency of the processing system.

The electrostatic charge between the wafer 6 and the support surface 14must be deactivated before the wafer may be safely removed from thesupport body 12. In a preferred embodiment, the electrodes 22 and 24 aredischarged by switching the electrodes from the voltage supply 42 to 47ground 47 through resistors 49 having a resistance of about 100 Ω. Theresistors control the rate of discharge, preventing the development ofvoltage transients which may damage the components on the wafer surface.The application of any RF bias to the support system 10 is alsodiscontinued. During this time, the plasma source of the processingsystem remains active causing any charge remaining in the wafer todrain. By effectively grounding the electrodes 22 and 24 and the wafer6, the electrostatic field is removed and the wafer may be easily andsafely removed from the support surface 14.

In the present embodiment, the support system 10 is particularly adaptedfor use with plasma-enhanced processing systems. Electrode assembly 20includes means for applying an RF bias to the support body. As is shownparticularly in FIG. 6, electrode assembly 20 includes an electricalconnector 52 which couples the inner and outer electrodes 22 and 24,respectively, to an RF source 54 through a matching network 56. Theself-induced bias created on the wafer by applying the RF bias to thesupport surface accelerates ions from the plasma sheath toward thewafer. These energized ions are required to prevent formation of voidsduring step coverage chemical vapor deposition.

The frequency of the RF bias applied to the support surface 14 is withinthe range of 450 kHz to 60 MHz. Preferably, the RF frequency of theplasma source is different from that of the chuck to minimize frequencybeating. In the present embodiment, the frequency of the RF source 54 isapproximately 3.39 MHz for a plasma source frequency of approximately13.56 MHz.

A preferred matching network 56 is shown schematically in FIG. 6. Thematching network 56 generally includes an inductor 57 and a pair ofvariable capacitors 58 and 59 coupled to the inductor 57 for phasematching the RF source 54 to the wafer 6 to change the RF deliverypattern to the wafer. The support body 12 has a well defined, capacitiveinductance of about 4-7 Ω at 50° to 75° C. during the process. The rangeof the adjustable capacitors 58 and 59 and the inductor 57 have beendesigned such that, if no plasma is present, the match is out of rangecausing the RF generator to reduce its output level to prevent damage tothe support assembly 10 due to excessive voltage in the unloadedresonant circuit. The inductor 57 has an iron powder core material forminimizing inductance loss. The high permeability of the powder reducesthe number of turns which are required, improving the Q value and spacerequirements of the inductor. For an RF source frequency of about 3.39MHz, the inductor 57 preferably has an inductance of about 13 μH.Matching network 56 is preferred as it offers an increase in efficiencyof about fifty percent compared to standard systems. However, it is tobe understood that in other modifications of the invention other typesof matching networks may be employed.

In a preferred embodiment of the invention, the DC voltage source 42 andthe RF bias source 54 are combined as shown in FIG. 6. Both sources 42and 54 are coupled directly into the electrodes 22 and 24, with the DCvoltage source 42 being tied to the same connection through an RCfilters 43 and 45. Combining the DC source 42 and RF source 54 reducesthe number of connections to the support body, minimizing the overallsize required for the support body 12. This is of particular advantagewith the present invention, where raising the support body 12 above thebottom of the chamber limited the amount of available space. Capacitors62 positioned between the RF source 54 and the electrodes 22 and 24control the ratio of the application of the RF bias to the innerelectrode 22 and the outer electrode 24, providing an adjustmentmechanism for obtaining a uniform RF distribution across the entirewafer for ensuring uniform processing on the wafer surface.

As is set forth above, the guard ring 26 may be coupled to the centertapof the DC voltage source 42 when support system 10 is used withplasma-enhanced processing systems to provide a uniform DC voltageacross the wafer. In addition, the guard ring 26 may be tied to the RFsource 54 to provide a means of further controlling the RF biasdelivered to the wafer plane.

The guard ring 26 may be formed of an electrically conductive materialsuch as aluminum. By tying the electrically conductive guard ring 26 tothe RF source as shown for example in FIG. 6, a direct measurement ofthe induced wafer bias may be obtained at junction 64 when theelectrical contact with the wafer is established.

Support body 10 includes an ion focus ring 72 which extends around theperiphery of the electrode assembly 20 to protect the active electrodesfrom the plasma. The ion focus ring 72 is formed of a ceramic materialor other suitable dielectric material. As is shown particularly in FIG.7, the wafer extends across the guard ring 26 and a portion of the ionfocus ring 72. In the present embodiment, the ion focus ring 72 includesan annular shoulder 74 for supporting the wafer so that the ion focusring 72 at least partially protects the peripheral edge of the waferfrom the plasma. Any plasma seeping between the wafer and the ion focusring 72 will encounter the guard ring 26, which will effectively isolatethe plasma from the active electrodes 22 and 24.

Wafer 6 is lowered onto and raised from support surface 14 by a waferlifting assembly, generally designated 86. Lifting assembly 86 includesa plurality of lifting pins 88 which extend through apertures 90 formedin the support surface 14 and the electrode assembly 20. The liftingpins 88 are movable between the extended position shown in FIG. 4, withthe pins 88 retaining the wafer 6 above the support surface 14, and theretracted position shown in FIG. 8. In the present embodiment, liftingmechanism 86 includes three lifting pins 88 (FIG. 1), the minimum numberof pins required for evenly supporting wafer 6 as it is moved relativeto the support surface. Pins 88 are located approximately halfwaybetween the center and peripheral edge of the wafer. Although using aminimum number of pins is preferred, it is to be understood that thenumber and position of pins 88 and apertures 90 may be varied asdesired.

In the present embodiment, the three lifting pins 88 are carried by ayoke member 92. The yoke member 92 is moved back and forth relative tothe support surface 14, moving the lifting pins 88 between the extendedand retracted positions shown in FIGS. 4 and 8, by an actuator 94disposed between the electrode assembly 20 and yoke member 92. Movementof the lifting pins 88 is synchronized with the yoke member 92, ensuringthe wafer 6 is retained in a substantially horizontal orientation as itis moved by the lifting pins 88. The actuator 94 of the presentembodiment is provided by a pneumatic cylinder, although it will beunderstood that other actuating means may also be used to raise andlower the yoke member 92.

As is shown particularly in FIG. 8, lifting pin 88 is mounted to acollar 96. In the present embodiment, collar 96 is preferably formed ofa plastic material for increased compliance and reduced friction as thepin 88 is moved between the retracted and extended positions. Thelifting pin 88 and collar 96 extend through the longitudinal bore of abearing 98. In the present embodiment, the bearing 98 is positioned inan opening 99 formed in the base 28 of the electrode assembly 20. Ashaft 100 couples the collar 96 to a socket 102 carried by the yokemember 92. The collar 96, shaft 100 and socket 102 are surrounded by abellows assembly 104 which is mounted to the electrode assembly 20 andthe yoke member 92. Suitable seal rings are compressed between bellowsassembly 104 and the electrode assembly and yoke member. The bellowsassembly 104 expands and contracts and the yoke member 92 is raised andlowered relative to the electrode assembly 20. As is described in moredetail below, the lifting mechanism 86 of the present invention is ofparticular advantage in that it cooperates with the wafer cooling systemin the delivery of a gaseous substance to the support surface 14. Itwill be understood that the various components of the lifting mechanism86 may be varied within the scope of the present invention. Moreover, itwill be understood that in other modifications of the invention, supportsystem 10 may employ different mechanisms for removing the wafer 6 fromthe support surface.

Support system 10 employs a gaseous cooling system for cooling the waferduring processing. A non-reactive gaseous substance, such as helium,argon, oxygen, hydrogen and the like, is distributed between the supportsurface 14 and the wafer 6 to provide substantially uniform coolingacross the entire wafer. Maintaining the entire wafer at a uniformtemperature during processing significantly improves the uniformity ofthe layers formed on the wafer surface.

In the present embodiment, the gaseous substance is delivered throughthe lifting mechanism 86 to the support surface 14. The gas source 114is coupled to the yoke member 92 of the lifting mechanism via conduit115. The yoke member 92 is formed with a channel network 116, shownparticularly in FIG. 9, for distributing the gaseous substance betweenthe three lifting pins 88. The gaseous substance enters through a gasinlet 118 and travels through the channel network 116 along the legs ofthe yoke member 92 to socket 102. The socket 102 has a hole 120 formedtherein which extends inwardly to the interior cavity 122 of the socket.The shaft 100 fits loosely within the socket cavity 122, providing apassageway for the gaseous substance between the shaft 100 and thesocket 102. The gaseous substance flows upwardly around the shaft 100into the interior of the bellows assembly 104. From the bellows assembly104, the gas flows between the collar 96 and the bearing 98 and upwardlythrough the aperture 90 formed in the electrode assembly 20 to thesupport surface 14. The apertures 90 extending through the electrodeassembly 20 are coated with a dielectric material to isolate the DCvoltage from the gaseous substance. Preventing exposure of the gaseoussubstance to the DC voltage is of particular importance to preventarcing.

Transporting the gaseous substance through the lifting assembly 86 is ofparticular advantage in that the number of holes formed in theelectrodes is minimized. This is particularly desirable in that itimproves the reliability of the electrode assembly 20 by minimizingareas of possible arcing when the support system 10 is used in aplasma-enhanced processing system. Minimizing the number of holes alsoreduces the manufacturing costs of the support body 12. The apertures 90are particularly suitable for uniformly delivering gas to the supportsurface 14 because of the symmetrical arrangement of lifting pins 88 andapertures 90.

The cooling system of the present invention includes means forpreventing catastrophic separation of the wafer 6 from the support body12 during processing. As is shown particularly in FIG. 10, the outerdiameter of the collar 96 of the lifting pin 88 is substantially equalto the inner diameter of the longitudinal bore of the bearing 98. Alongitudinally-extending shallow groove 126 formed in the interior wallof the bearing 98 and a longitudinally-extending shallow groove 128 onthe exterior of the collar 96 provide a conduit for the gaseoussubstance between the bellows assembly 104 and the apertures 90.Although the grooves 126 and 128 are substantially aligned in thepresent embodiment, the grooves 126 and 128 may also becircumferentially spaced relative to one another if desired. The shallowgrooves 126 and 128 provide a restriction which significantly reducesthe flow rate of the gaseous substance. The restriction divides the gasflow path into a first plenum between the gas source 114 and the bearing98 and a second plenum between the bearing and the support surface, withthe second plenum containing only a fraction of the available gas toreducing the amount of available gas proximate the support surface 14.

In some instances, the electrostatic charges between the wafer and thesupport surface may be partially disrupted during processing. In theevent a portion of the wafer becomes separated from the support surface,the gas in the second plenum will bleed through the resulting gap intothe processing chamber. If the entire gas supply was exposed to thesupport surface, the pressure would cause the wafer to be forced fromthe support surface 14. This catastrophic separation of the wafer fromthe support surface is prevented because of the limited volume of gas inthe second plenum. After the gaseous substance in the second plenum hasescaped, the wafer is free to fall back against the support surface andbecome reattached to the support body. With the restriction provided bythe shallow grooves 126 and 128, possible damage to the wafer because ofpartial loss of the electrostatic charge is substantially eliminated.

In the present embodiment, the restriction is provided by the shallowgroove 126 formed in the interior of the bearing 98 and the shallowgroove 128 formed on the exterior of the collar 96. However, it is to beunderstood that the position of the restriction relative to the supportsurface may be varied if desired. Moreover, other means may be used torestrict the flow of gas between the gas source 114 and the supportsurface 14 within the scope of the present invention. Because of therestriction, additional time is required for the second plenum and thespace between the wafer and the support surface 14 to fill with gas. Asa result, the wafer may quickly reach the desired processingtemperature. Another advantage of the restriction is that it provides acapillary feed which prevents arcing in the event you have a highpotential difference between the support surface 14 and the liftingmechanism 86.

Although not shown, with the support body of the present invention, thegaseous substance used for cooling the wafer during processing may alsobe used to raise and lower the lifting pins 88. In the modifiedembodiment, the lifting pins 88 are carried by a suitable supportstructure and coupled to a spring. The pressure of the gaseous substanceand the springs control movement of the lifting pins between theextended and retracted positions shown in FIGS. 4 and 8.

The support surface 14 of the present invention includes means foruniformly distributing the gaseous substance across the entire wafer. Asis shown particularly in FIG. 3, a plurality of gas distribution grooves136 are formed in the support surface 14. In the present embodiment, thelocation of the apertures 90 coincide with the grooves so that the gasis fed directly into the gas distribution grooves. The gas then flowsthrough the grooves and into the spaces between the rear surface of thewafer and the support surface 14. The grooves 136 preferably divide thesupport surface 14 into a plurality of segments 138, with the totalsurface area of each of the segments being substantially equal. In thepresent embodiment, the groove configuration includes six radiallyextending grooves positioned at sixty degree intervals around thecircumference of the wafer and five circumferentially extending grooves.When the support body 12 is used to retain an eight inch wafer, thesegments 138 each have a surface area of about 1.5 to 2.5 square inches,for example two square inches. However, it will be understood that agreater or lesser segment surface area is within the scope of thepresent invention. The configuration of the gas distribution grooves 136provides for a substantially uniform distribution of gas across theentire support surface so that the wafer may be subjected to uniformcooling throughout the process.

The configuration of the grooves is of particular importance to avoidignition of the gaseous substance due to the existence of potentialbetween the wafer and the electrode especially in plasma-enhancedsystems. The width of the groove measures approximately 0.031 to 0.125inches, preferably about 0.062 inches, while the maximum depth isapproximately 0.010 to 0.031 inches, preferably about 0.015 inches. Asis shown particularly in FIG. 11, the grooves 136 are curved. The edgesof the grooves have a radius of curvature R1 in the range of 0.031 to0.062 inches while the radius of curvature R2 of the grooves is in therange of 0.031 to 0.093 inches. In the present embodiment, the outergroove edges preferably have a radius of curvature of about 0.045 incheswhile the radius of curvature of the groove is about 0.062 inches. Withthese dimensions, ignition of the helium employed in the presentembodiment is substantially avoided.

With the support system 10 of the present invention, arm members 16mount the support body 12 to the processing chamber with the supportbody spaced from the bottom of chamber as is shown for example in FIG.1A. Removing the support body 12 from the bottom of the chamber offersincreased flexibility in the design of the overall processing system.For example, the pump (not shown) may be axially aligned with thesupport body 12, minimizing the footprint of the overall system andimproving the effectiveness of the pump during processing. In thepresent embodiment, support system 10 includes two arms 16A and 16Bextending toward one wall of the processing chamber 8. However, it is tobe understood that the number of arms may be increased or, if desired,only one arm member may be used as is shown for example in FIG. 2A.Using a plurality of arm members offers several advantages, includingincreased stability and reduced size. The reduced diameter of the armmembers 16 reduces the amount of interference with the symmetry of theflow of gases to the pump. This is particularly important for pressuresensitive applications. In the present embodiment, arm members 16A and16B are mounted to one wall of the chamber 8 as is shown in FIG. 2.However, it is to be understood that the arm members may also extendtoward the corners of the processing chamber or to different chamberwalls if desired.

Arm members 16 are each formed with a longitudinally extending bore 144.As is schematically illustrated in FIG. 2, the bore of one of the armmembers 16A provides a conduit from the support body 12 for theelectrical connectors 40 and 44 coupling the electrodes 22 and 24 to thevoltage source and the electrical connector 52 coupling the RF source 54to the electrodes. The gas source 114, the fluid source 36 for theelectrodes assembly 20 are connected to the support body 12 throughconduits 115 and 35, respectively, which extend through the bore 144 ofthe other arm member 16B. Although not shown, the pneumatic lines foroperating the actuator 94 also extend through the bore 144 of the armmember 16B. By using two arm members 16, the electrical components aresafely separated from the liquid cooling fluid as well as the gaseoussubstance used to cool the wafer.

As is shown in FIGS. 1 and 1A, in the present embodiment arm members16A, 16B are preferably mounted to a support plate 150 of carriagestructure 17. The support system 10 is installed by inserting thesupport body 12 and arm members 16 through an opening formed in thechamber wall and securing the support plate 150 to the exterior of thechamber with suitable fasteners. The support body 12 may be convenientlyremoved by disengaging the support plate 150 from the chamber exteriorand pulling the entire unit from the chamber. A housing 152 mounted tothe opposite side of the support plate 150 encloses components of thesupport system 10 such as RF/DC combiner, match network and DC supply.Coupling members (not shown) couple the fluid source 36 for cooling theelectrode assembly 20 and the gas source 114 for cooling the wafer 6 tothe conduits 35 and 115, respectively. A track structure 154 supportsthe support plate 150 and housing 152, facilitating movement of thesupport plate 150 for insertion of the support body 12 into or removalof the support body from the chamber.

With carriage assembly 17, support body 12 may be efficiently andconveniently positioned in and removed from the processing chamber. Thecarriage assembly 17 improves the accessibility of the chamber formaintenance and clean-up of a fractured wafer. Manufacture of theprocessing chamber is simplified as the arm members 16 may be mounted tothe carriage structure and the necessary connections completed outsideof the processing chamber. Although use of the carriage assembly 17 ispreferred, it is to be understood that the assembly may be omitted andthe arm members 16 mounted directly to the chamber wall.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best use the inventionand various embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. An electrostatic support system for retaining awafer in a processing chamber having a chamber wall and a bottom, saidsupport system comprising:a body portion having a support surface forretaining said wafer, at least one arm member extending between saidbody portion and the chamber wall for supporting said body portion inthe processing chamber with said body portion spaced inwardly from thechamber wall and said body portion and said at least one arm memberspaced above the bottom of the chamber, said at least one arm memberhaving at least one longitudinally extending passageway formed therein,said at least one passageway extending between said body portion and thechamber wall, and an electrostatic system for applying a charge to saidsupport surface for electrostatically coupling said wafer to saidsupport surface, said electrostatic system including at least oneelectrode carried by said body portion and at least one electrostaticelectrical connector positioned in electrical contact with saidelectrode, said electrostatic electrical connector being positioned insaid at least one passageway formed in said arm member such that saidelectrostatic electrical connector is substantially isolated from saidchamber.
 2. The support system of claim 1, and further comprising acarriage assembly for mounting said electrostatic support system to thewall of the processing chamber, said at least one arm member beingmounted to said carriage assembly.
 3. The support system of claim 1, andfurther comprising a biasing system for applying an RF bias to said bodyportion.
 4. The support system of claim 3 in which said biasing systemincludes at least one biasing electrical connector positioned in said atleast one passageway formed in said arm member such that said biasingelectrical connector is substantially isolated from the chamber.
 5. Thesupport system of claim 1, and further comprising a wafer cooling systemfor cooling said wafer.
 6. The support system of claim 5 in which saidwafer cooling system includes at least one coolant passageway extendingthrough said body portion for circulating a cooling fluid therethroughand at least one conduit coupled to said coolant passageway, saidconduit being positioned in said at least one passageway of said armmember such that said coolant passageway is substantially isolated fromthe chamber.
 7. The support system of claim 6 in which said conduit andsaid electrostatic electrical connector extend through separatepassageways.
 8. The support system of claim 1 in which said body portionincludes at least one lifting member movable relative to said supportsurface between an extended position with said lifting member extendingthrough a hole in said support surface for supporting said wafer abovesaid support surface and a retracted position with said lifting memberretracted beneath said support surface.
 9. An electrostatic substratesupport system mountable in a processing chamber having a chamber walland a bottom, said support system comprising:a body portion having asupport surface for retaining the substrate and at least one coolantpassageway formed therein for circulating a coolant fluid through saidbody portion; at least one electrode carried by said body portion forelectrostatically coupling the substrate to said support surface; atleast one arm member coupled to said body portion, said at least one armmember extending between said body portion and the chamber wall forsupporting said body portion in the processing chamber with said armmember and said body portion spaced above the bottom of the chamber;first and second passageways extending through said at least one armmember between said body portion and the chamber wall, said firstpassageway housing at least one electrostatic electrical connector forcoupling said at least one electrode to a voltage source outside of thechamber and said second passageway housing conduits for coupling saidcoolant passageway to a coolant source outside of the chamber.
 10. Thesupport system of claim 9 in which said body portion includes a gasdelivery network for delivering a gaseous substance to said supportsurface, and said second passageway housing at least one gas deliveryconduit for coupling said gas delivery network to a gas source outsideof the chamber.
 11. The support system of claim 9 in which said firstpassageway houses at least one biasing electrical connector for couplingsaid electrode to a biasing source for applying an RF bias to said bodyportion.
 12. The support system of claim 9 in which two arm portions arecoupled to said body portion, said first passageway being formed in oneof said two arm portions and said second passageway being formed in theother of said two arm portions.
 13. The support system of claim 9, andfurther comprising a carriage assembly for mounting said support systemto the chamber wall, said at least one arm member being mounted to saidcarriage assembly.